System for, and method of, providing a header and a trailer in data packets

ABSTRACT

Each packet normally consists of a preamble, start-of-frame delimiter and data. The preamble has nibbles each having a particular format. A header substituted for preamble nibbles by an individual one of the originating devices in a plurality, and an individual one of the ports in such originating device, indicates such originating device and such port. Such port in such originating device sends such modified packet to others of the originating devices and to an observing station. The header format is such that the last nibble in the header and the remaining preamble portion will not be confused with any two (2) nibbles in the header. A particular one of the originating devices indicated in the data converts the header back to the preamble format and transmits the converted packet to a receiving station. The observing station records the individual originating device, and the individual port in such device, indicated in the header. Each packet includes at its end a trailer formed from a plurality of nibbles and indicating whether or not a collision has occurred between such packet and a packet from another one of the originating devices. The trailer in each packet may also indicate additional information--e.g. whether the packet (a) is a normal packet originally formed, (b) is a runt packet, (c) is from an unacceptable source and (d) the delay between each packet end and the next packet start. The information in the trailer for each packet passes to the observing station.

This invention relates to a system for, and method of, providing aheader for indicating to an observing station an individual one of aplurality of originating devices, and an individual one of the ports insuch originating device, providing packets of data. The invention alsorelates to a system for, and a method of, providing a trailer forindicating whether a collision has occurred between the transmission ofpackets from such individual one of the ports in such individual one ofthe originating devices and packets from another one of the originatingdevices.

BACKGROUND OF THE INVENTION

Systems are provided for transmitting data in packets. Each packet mayhave at least a particular length (e.g. at least 512 nibbles) where eachnibble consists of a plurality (e.g. four (4)) binary bits. Each packetmay include a preamble, a start-of-frame delimiter and data. Thepreamble in each packet is provided to synchronize the subsequentnibbles in the packet with clock signals. The preamble may consist of aplurality of nibbles each having the same particular format. Thestart-of-frame delimiter includes a plurality of nibbles indicating thatdata follows such delimiter. In addition to providing information, thedata may include an identification of the source of the packet and therecipient of the packet.

It is sometimes desired to make a record of the individual one of theoriginating devices, and the individual one of the ports in suchoriginating device, providing the packets. Two (2) different approacheshave been provided in the prior art to record such information. Oneapproach has been to provide additional signal lines to record theindividual one of the originating devices, and the individual one of theports in such originating device, providing the packets. The use of suchadditional signal lines is not satisfactory because it undulycomplicates the construction of the system. A second approach has beento provide a trailer at the end of the packet to indicate the individualone of the originating devices and the individual one of the ports insuch originating device. This is not desirable because it shortens thespace between successive packets.

Sometimes two (2) originating devices transmit packets at the same time.This causes a collision to occur between the two (2) packets. Any otheroriginating device simultaneously receiving the two (2) packets willbecome confused and accordingly generate wrong information. It isdesirable to record the occurrence of such a collision. It is alsodesirable to record other information upon the occurrence of acollision. This would include the spacing between successive packets andindications of a normal packet or variations from a normal packet. Noone until now has used the same lines normally used for passing thepacket in order to record the occurrence of collisions, the spacingbetween packets and indications for each packet that the packet isnormal or varies in specified ways from a normal packet.

BRIEF DESCRIPTION OF THE INVENTION

This invention provides a system for, and method of, providing andrecording the different information specified *above. For example, thesystem and method of this invention provide such information in arelatively straightforward manner without complicating the constructionof the system. The system and method of this invention illustrativelyprovide for a recording of the individual one of the originating devicesin a plurality, and the individual one of the ports in such originatingdevice, providing packets of information. The system and method of thisinvention also provide for the determination of collisions betweenpackets simultaneously transmitted from two (2) of the originatingdevices in the plurality and for the indication of the occurrence ofsuch collisions.

In one embodiment of the invention, each packet normally consists of apreamble, a start-of-frame delimiter and data. The preamble has nibbleseach having a particular format. A header substituted for preamblenibbles by an individual one of the originating devices in a plurality,and an individual one of the ports in such originating device, indicatessuch device and such port in such originating device. Such port in suchoriginating device sends such modified packet to others of theoriginating devices and to an observing station.

The header format is such that the last nibble in the header and theremaining preamble portion will not be confused with any two (2) nibblesin the header. A particular one of the originating devices indicated inthe data converts the header back to the preamble format and transmitsthe converted packet to a receiving station. The observing stationrecords the originating device, and the port in such device, indicatedin the header.

Each packet includes at its end a trailer formed from a plurality ofnibbles and indicating whether or not a collision has occurred betweensuch packet and a packet from another one of the originating devices.The trailer in each packet may also indicate additionalinformation--e.g. whether the packet (a) is a normal packet, (b) is arunt packet, (c) is from an unacceptable source and (d) the delaybetween each packet end and the next packet start. The information inthe trailer for each packet passes to the observing station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the different portions of an informationpacket normally transmitted in the prior art;

FIG. 2 is a diagram showing the different portions of an informationpacket modified in accordance with the concepts of this invention, suchdifferent portions including a header for indicating an individual oneof a plurality of originating devices, and an individual one of theports in such originating device, sending such packet;

FIG. 3 is a table showing how the header indicates the individual one ofthe plurality of originating devices and the individual one of the portsin such originating device;

FIG. 4 is a diagram, similar to that shown in FIGS. 1 and 2, of thedifferent portions of a packet and includes a header and also includes atrailer at the end of the packet for indicating the occurrence of acollision resulting from a simultaneous transmission of packets from two(2) of the originating devices in the plurality and also includes awaveform showing the transmission of the signals in the packet when nocollision occurs;

FIG. 5 is a table similar to that shown in FIG. 3 and shows how thetrailer in the packet indicates a lack of a collision between packetsand also indicates other specific data;

FIG. 6 is a table showing how different data other than the occurrenceor lack of occurrence of a collision are indicated in the table shown inFIG. 5;

FIG. 7 is a diagram, similar to that shown in FIG. 4, of a packet with aheader and a trailer and shows the signal waveform produced in thepacket upon a lack of occurrence of a collision between this packet andanother packet and additionally shows the signal waveform produced inthe packet upon the occurrence of a collision;

FIG. 8 is a table showing the pattern of signals produced in the trailerin a packet when there is a collision between this packet and thesimultaneous transmission of another packet;

FIG. 9 is a block diagram of circuitry for detecting collisions betweenpackets simultaneously transmitted by a pair of originating devices;

FIG. 10 is a schematic circuit diagram showing in block form a pluralityof originating devices on a pair of printed circuit boards for receivingand transmitting packets of information and further showing an observingstation on another printed circuit board for recording the informationin the headers of packets transmitted by an individual one of theoriginating devices and by an individual one of the ports in suchoriginating device;

FIG. 11 is a circuit diagram showing in additional detail a pair of theoriginating devices shown in FIG. 10 and also showing in additionaldetail the circuit interrelationships between the originating devicesand the observing station;

FIG. 12 is a detailed circuit diagram in block form of one of the datamultiplexers shown as a single block in the circuit diagram of FIG. 11;

FIG. 13 is a detailed circuit diagram in block form of an expansioncontroller and arbiter shown as a single block in the circuit diagram ofFIG. 11;

FIG. 14 is a detailed circuit diagram in block form of an expansionstate machine shown as a single block in the circuit diagram of FIG. 13;

FIG. 15 is a circuit diagram in block form and shows in additionaldetail a data forwarding stage shown as a single block in FIG. 11;

FIG. 16 is a detailed circuit diagram in block form of a start-of-framedetect stage shown as a single block in FIG. 15;

FIG. 17 is a detailed circuit diagram in block form of a data processorshown as a single block in FIG. 11;

FIG. 18 is a detailed circuit diagram in block form of a data processingstate machine shown as a single block in FIG. 17;

FIG. 19 is a table specifying the definitions of various terms used inthe previous figures; and

FIG. 20 shows voltage wave forms at strategic terminals in circuitryincluded in some of the previous Figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of an information packet, generally indicatedat 10, normally provided in the prior art. The packet is formed from aplurality of nibbles each formed from a plurality of binary bits. Forexample, each nibble may be illustratively formed from four (4) binarybits which may be provided in a parallel relationship. The packet 10 maybe provided with an idle portion 12, a preamble 14, a start-of-framedelimiter 16, data 18 and a trailer 20.

The preamble 14 is provided at the beginning of the packet 10 tosynchronize the presentation of the successive nibbles in the packetwith a clock signal. Each nibble 14 in the preamble may have the sameformat as the other nibbles in the preamble. For example, each nibble inthe preamble may indicate an analog value of "5" in hexadecimal codedform.

The start-of-frame delimiter 16 indicates the beginning of the dataportion 18 of the packet 10. It is provided in a particular pattern. Itis followed by the data portion 18 of the packet 10. The data portion 18provides the information in the packet. It may also indicate the sourcefrom which the packet 10 is provided. It may additionally indicate thestation which is to receive the packet.

In one embodiment of the invention, a plurality of integrated circuitboards generally indicated at 24 and 26 in FIG. 10 may be provided.Although only two (2) boards 24 and 26 are shown in FIG. 10, it will beappreciated that a considerably greater number of boards than two (2)may be provided.

Each of the boards such as the boards 24 and 26 may have a substantiallyidentical construction. Each of the boards 24 and 26 may include aplurality of integrated circuit chips 30. Each of the chips 30 may havea substantially identical construction. For example, each of the chips30 may constitute a 5205 chip developed by, and fabricated for,applicant's assignee of record in this application.

Each of the chips 30 may be considered to constitute an originatingdevice. The cumulative number of originating devices 30 on the boards 24and 26 may be considered to constitute a plurality. Each of theoriginating devices 30 has a plurality of ports 32. The packets 10 passinto an individual one of the originating devices 30 through anindividual one of the plurality of ports 32 in such individual one ofthe originating devices.

As previously described, the packets 10 include the trailer 20 in oneform of the prior art shown in FIG. 1. The trailer 20 indicates anindividual one 30a of the originating devices 30 and the individual one(e.g. 32b) of the ports 32 for passing the packets from such originatingdevice. The packets 10 pass to an observing station 34 which records theindividual one 30a of the originating devices 30, and the individual one(e.g. 32b) of the ports 32 in the originating device 30a, through whichthe packets pass. As will be appreciated, it would be better not toprovide the trailer 20 at the end of the packets 10 to record theoriginating device 30a and the port 32b because this constitutes aninefficient use of the space between successive packets.

FIG. 2 shows packets generally indicated at 40. The packets 40 have beenmodified by applicants from the packets 10 of the prior art to obtainthe advantages of this invention. As will be seen, the packets 40 aresubstantially identical to the packets 10 except that they substitute aheader 42 for a portion of the preamble 14. Furthermore, a trailer 44 isincluded at the end of the packets 40 but the trailer 44 providescompletely different functions than the trailer 20 in the packets 10 andprovides these different functions on a more efficient basis than in theprior art. This will be described in detail subsequently.

The header 42 may be formed from four (4) nibbles respectivelydesignated as H1, H2, H3 and H4. They constitute substitutions for thefirst four (4) nibbles in the preamble 14 in the packets 10. The nibblesH1, H2, H3 and H4 are not used to provide a synchronization with theclock signals. They are used to indicate the originating device 30a, andthe port 32b in the originating device 30a, through which the packets 40pass.

FIG. 3 is a table indicating the format of the header 42 formed by thenibbles H1, H2, H3 and H4. As will be seen, each of the nibbles H1, H2,H3 and H4 may illustratively be formed from four (4) binary bits. Itwill be appreciated that a different number of bits than four (4) may beused to define each nibble without departing from the scope of theinvention. Six (6) of the binary bits in the table are respectivelydesignated as "PG15", "PG14", "PG13", "PG12", "PG11" and "PG10". Theseindicate an individual one of sixty-four (64) different originatingdevices 30. Four (4) of the binary bits in the table are respectivelydesignated as "PID3", "PID2", "PID1" and "PID0". These indicate anindividual one of sixteen (16) possible different ports in theindividual one of the originating devices represented by thedesignations "PG15"-"PG10".

It is desirable that the four (4) binary bits in the nibble H4 and inthe first nibble in the remaining portion of the preamble 14 have apattern different from the binary bits in any two (2) successive nibblesin the start-of-frame delimiter 16. This prevents any confusion fromarising between the header and the preamble in the packet 40 on the onehand and the start-of-frame delimiter in such packet on the other handwhen the information in the packet 40 is processed. It is also desirablethat the last nibble in the header and the remaining preamble portionwill not be confused with any two (2) nibbles in the header.

As indicated previously, the packets 40 pass from the originating device30a to all of the other originating devices 30 in the plurality. Thepackets 40 may pass through an originating device 30b in accordance withthe instructions from the external source (not shown). However, beforethe packets 40 pass through the originating device 30b, the header 42represented by the nibbles H1, H2, H3 and H4 is converted in theoriginating device 30b to the particular pattern in the preamble 14.

The packets 40 also pass to the printed circuit board 34. The printedcircuit board 34 may be considered to provide an observing station. Itincludes an integrated circuit chip designated as the 5205 byapplicants' assignee of record in this application and developed by, andfabricated for, such assignee. The observing station 34 processes theinformation in the header 42 and, from such processing, determines theidentity of the originating device 30a, and the individual one of theports 32b in such originating device, through which the packets 40 pass.The observing station 34 then records, in a memory 52 indicated as"statistics" in FIG. 17, the identity of the originating device 30a andthe individual one of the ports 32b in such originating device. Theobserving station 34 also detects and records whether any informalities(e.g., the delimiter) are missing from the packet.

The trailer 44 in the packets 40 provides a different function than thetrailer 20 in the packets 10. As shown in FIGS. 4 and 20, an expansiondata valid (XDV) signal 60 is produced at the beginning of the header 42in the packets 40. The expansion data valid signal 60 then continuesuntil the end of the data 18. When there is no collision as a result ofa simultaneous transmission of packets from the originating device 30aand another one of the originating devices 30, the XDV signal is negatedduring the production of the trailer 18 represented by the nibbles T1,T2, T3 and T4. The failure to produce a collision can be seen from FIG.4 in the line designated as "XDV" since no signal is produced during thenibbles T1, T2, T3 and T4.

FIG. 5 provides a table showing the signals which are produced duringthe nibbles T1, T2, T3 and T4 when there is no collision between apacket from the originating device 30a and a packet from another one ofthe originating devices 30. In this table, the successive designations"IPG5" to "IPG0" indicate the gap between successive pairs of thepackets 40 from the originating device 30a.

In FIG. 5, four (4) nibbles "CS3-C50" are provided. These nibblesprovide a check sum to indicate whether the nibbles H1-H4 and thenibbles T2 and T3 constitute proper indications. These nibbles haveproper indications when the values provided in these nibblescumulatively have a particular value. This is well known in the priorart.

The designations "EV1" and "EV0" in the table shown in FIG. 6 arecombined to provide several different indications which representseveral different special situations. Illustrative examples of thesespecial situations are shown in FIG. 6 and discussed below but otherexamples of these special situations may be provided without departingfrom the scope of the invention.

When the binary bits EV1 and EV0 in FIG. 6 are both zero (0), a normalpacket such as indicated at 40 may illustratively be provided. When thebinary bit EV1 is 0 and the binary bit EV0 is 1, a runt frame or packetmay illustratively be indicated. A packet generally consists of at least128 nibbles. When the number of nibbles in the packet 40 is less than128, a runt frame or packet is indicated. A runt frame or packet isgenerally not processed. However, sometimes a runt frame or packet issent to a separate receiver to control internal features in thereceiver. The runt frame or packet then instructs that receiver how tohandle certain calls to that receiver.

A binary value of 1 for EV1 and a binary value of 0 for EV0 in FIG. 6may illustratively indicate to the observing station 34 that the packetbeing received at the observing station is from an unacceptable source.Binary values of 1 for each of EV1 and EV0 may illustratively indicatethat the packet 40 is malformed. For example, the packet 40 may bemissing the start-of-frame delimiter 16.

The table shown in FIG. 5 includes a column designated as "XERR". Thiscolumn indicates whether there is a collision as a result of asimultaneous transmission of packets by the originating device 30a andby another of the originating devices 30. As will be seen, there is a"0" indication in the column XERR in FIG. 5 for each of the nibbles T1,T2, T3 and T4. This indicates that no collision has occurred.

FIG. 7 is similar to FIG. 4 except that it indicates a collision betweenthe packet 40 from the originating device 30a and a packet from one ofthe other originating devices 30. This may be seen by the production ofa collision signal 70, in the column designated as XERR in FIG. 7,during the production of the nibbles T2, T3 and T4. In the table shownin FIG. 8, the column designated as "XD" actually corresponds to thecolumns XD3, XD2, XD1 and XD0 in the table shown in FIG. 5.

When a collision occurs, all of the values in the columns XD3, XD2, XD1and XD0 become zero since the transmission of packets becomes halted inmidstream when a collision occurs. In this way, only a collisionindication is provided in the nibbles T1, T2, T3 and T4 when a collisionoccurs. This is indicated by a binary "0" in the nibble T1 and by abinary "1" in each of the nibbles T2, T3 and T4. A binary "0" isprovided in the nibble T1 in the XERR column to maintain compatibilitywith the first nibble for a normal trailer.

FIG. 9 is a circuit diagram schematically illustrated at 80 and showinga system for indicating how two (2) originating devices 30a and 30coperate to indicate a collision between packets simultaneouslytransmitted by such originating devices. The system 80 indicates anexpansion bus 82 for passing the XDV and XERR signals (also shown inFIG. 8) and the XCLK and XDATA signals between the originating devices30a and 30c. XCRSOUT signals respectively pass from the originatingdevices 30a and 30c through lines 84a and 84b to "or" networks 86a and86b.

The XCRSOUT signals on the lines 84a and 84b indicate that an individualone of the originating devices 30a and 30c is about to transmit apacket. The XCRSOUT signal on one of the lines 84a and 84b indicates tothe other originating devices 30 (including the originating device 30c)that one of the originating devices (e.g. 30a) is about to transmit apacket. The XCRSOUT signal from the originating device 30a passesthrough the "or" networks 86a and 86b and XCRSIN lines 88a and 88b tothe originating devices 30a and 30c to indicate to such originatingdevices that the originating device 30a is about to send a packet.

The XCRSOUT signal is indicated at 90 in FIG. 20. The XCRSOUT signal 90is generated by a clock on one of the printed circuit boards (e.g. theboard 24 in FIG. 10). This clock is different from the clock (XCLK) onthe expansion bus 82. The XCLK signal is indicated at 92 in FIG. 20.Because of this, the XCRSOUT signal can be generated before thegeneration of the XCLK signals 92. An XDIR₋₋ 0 signal 94 is generated aparticular period of time after the generation of the XCRSOUT signal 90.The difference in time between the initiation in the generation of theXCRSOUT signal 90 and the XDIR₋₋ 0 signal 94 may be considered toconstitute a Collision Resolution Time. This difference in time isindicated at 95 in FIG. 20. The Collision Resolution Time is provided toallow other originating devices than the originating device 30a time toindicate to the originating device 30a that at least one of such otheroriginating devices will be transmitting a packet simultaneously withthe transmission of a packet by the originating device 30a.

FIG. 9 also shows XCOLOUT signals respectively passing through lines 96aand 96b from the originating devices 30a and 30c to a collision detectstage 98. The XCOLOUT signals indicate a collision as a result of asimultaneous transmission of packets by two originating devices such asthe originating devices 30a and 30c. XCOLIN signals respectively passfrom the collision detect stage 98 through lines 99a and 99b to theoriginating devices 30a and 30c. The XCOLIN signals indicate to theoriginating devices 30a and 30c that a collision has occurred as aresult of the simultaneous transmission of packets by such originatingdevices. As will be seen, the XCOLIN signals indicate to all of theoriginating devices 30 on the printed circuit boards 24 and 26 that acollision has occurred.

When the Collision Resolution Time 95 in FIG. 20 has expired without theoccurrence of an XCOLIN signal, the originating device 30a starts todrive the expansion bus 82 in FIG. 9 in providing data for transmissionto the other originating devices including the originating device 30c inFIGS. 9 and 10 as discussed above. This occurs when the XCLK line startsto provide clock signals as indicated at 92 in FIG. 20 and when theoriginating device 30a provides a data valid signal as indicated at 60in FIGS. 4 and 20. The originating device then provides the header 42,the remainder of the preamble 14, the start-of-frame delimiter 16, thedata 20 and the trailer 44 to the expansion bus 82. This is indicated at104 in FIG. 20. If the XCOLIN signal is asserted by the collision detectstage 98 at any time prior to the expiration of the Collision ResolutionTime (95 in FIG. 20), the expansion bus 82 remains undriven for theremainder of the packet from the originating device 30a.

It may sometimes happen that the XCOLIN signal is detected after theCollision Resolution Time has expired. When this occurs, the originatingdevice 30a driving the expansion bus 82 generates a collision trailer asindicated at 70 in FIGS. 7 and 20 and discontinues any driving of theexpansion bus 82. As will be seen at 70 in FIG. 20, the collisiontrailer 70 is generated as soon as a collision is detected as a resultof a simultaneous transmission of packets by the originating device 30aand one of the other originating devices 30.

A broken oval is indicated at 100 in FIG. 9 for the originating device30a. This broken oval encloses the line 88a (XCRSIN), the line 84a(XCRSOUT), the line 96a (XCOLOUT) and the line 99a (XCOLIN). This brokenoval also encloses the portion of the originating device 30a receivingsignals on the lines 88a, 84a, 96a and 99a. The portion of the systemwithin the broken oval 100 is designated as "Arbitration Interface." Itindicates the portion of the circuitry shown in FIG. 9 that arbitrateswhether a collision has or has not occurred.

One key to the backplane arbitration system shown in FIG. 9 anddescribed above is the Collision Resolution Time. The duration of thistime is set to be greater than the time required for the collisiondetect block 98 to signal XCOLIN to the originating devices 30a and 30cin the worst case in the operation of the system. If the algorithm forproviding a collision detect signal requires a time greater than theCollision Resolution Time, multiple ones of the originating devices 30will be able to drive the expansion bus 82 simultaneously, therebydestroying the signal integrity of the bus.

In applicant's embodiment of the invention, the observing station 34 inFIG. 10 does not maintain a record of collisions because the trailernibbles T1-T4 indicate that a collision has occurred. It will beappreciated, however, that it is within the scope of the invention forthe observing station 34 to indicate the occurrence of a collision. Atany rate, the trailer nibbles T1-T4 distinguish to the observing station34 between a collision and a runt frame or packet. In this way, theobserving station 30 records only a runt frame or packet and does notrecord a shortened packet resulting from a collision. Furthermore, theoriginating device 30a indicates a collision when the collision hasoccurred between a packet from the originating device 30a and one of theother originating devices 30 in the system.

FIG. 11 is a schematic circuit diagram of an expansion bus system whichincludes the originating devices 30a and 30c and includes the observingstation 34. The expansion bus 82 (also shown in FIGS. 9 and 10) isdivided into two (2) segments, one indicated at 82a and the otherindicated at 82b. The expansion bus 82a provides information relating tothe data valid (xdv) signal 60 in FIGS. 4 and 20, the clock (XCLK) 92 inFIG. 20 and the collision (XERR) signal 70 in FIGS. 7 and 20. Theexpansion bus 82b provides the xdata signals indicated at 104 in FIG.20. As will be seen, each of the expansion buses 82a and 82binterconnects the originating devices 30a and 30c and the observingstation 34. This interrelationship is known in the prior art and is notaffected in any way by the system or method of this invention. This isone of the advantages of the system of this invention.

Each of the originating devices 30a and 30c in FIG. 11 includes anexpansion controller and arbitration stage 104, a data multiplexer (MUX)106 and a data forwarding stage 108. The expansion controller andarbitration stage 104 provides much of the functions shown in FIG. 9 anddescribed above in connection with FIG. 9. The data multiplexer 106provides for a controlled passage of the header nibbles (H1-H4) and thetrailer nibbles (T1-T4). The data forwarding stage 108 provides for acontrolled transfer of the nibbles representing the data in each packet.The stages 104, 106 and 108 are shown in detail in subsequent Figuresand additional discussion relating to these stages will be providedsubsequently in connection with these Figures.

The observing station 34 includes a data processor 110 for providing acontrolled passage of the nibbles H1-H4 representing the header and thenibbles T1-T4 representing the trailer. The data processor 110 is shownin additional detail in FIGS. 17 and 18. Additional discussion relatingto the data processor 110 will be provided in connection with theseFigures.

The expansion controller and arbitration stages 104 in the originatingdevices 30a and 30c receive a data valid signal on lines 112a and 112b.This data valid signal is indicated at 60 in FIGS. 4, 7 and 20. Thestages 104 in the originating devices 30a and 30c respectively providethe XCRSOUT signals (also shown in FIG. 9) on the lines 84a and 84b tothe carrier and collision detect stage 114 and respectively provide theXCOLOUT signals (also shown in FIG. 9) on the lines 96a and 96b to thecollision detect stage. The carrier collision and detect stage 114corresponds to the detect stage 98 in FIG. 9.

The collision detect stage 114 in FIG. 11 respectively passes the XCRSINsignals on the lines 88a and 88b, and the XCOLIN signals (also shown inFIG. 9) on the lines 99a and 99b, to the data forwarding stage 104 inthe originating devices 30a and 30c. The data multiplexers 106 in theoriginating devices 30a and 30c in FIG. 11 respectively receive data(rxData) on lines 116a and 116b. The data forwarding stages 106 in theoriginating devices 30a and 30c respectively transmit data (txData) onlines 118a and 118b.

The data multiplexer (MUX) 106 (FIG. 11) is shown in additional detailin FIG. 12. It includes a plurality of multiplexers 120a-120i. Themultiplexer 120a has two (2) inputs, one constituting an "idle" and theother constituting received data (rxData). The passage of one or theother of these inputs through the multiplexer 120a is controlled by asignal on a dataSelect(idle) line 122a.

Each of the multiplexers 120b-120i respectively has a first input fromthe output of the previous stage. Each of the multiplexers 120b-120irespectively has a second input from an individual one of lines124b-124i. The lines 124b-124e are respectively designated as hdr1-hdr4.They provide the header nibbles H1-H4. The lines 124f-124i arerespectively designated as trlr1-trlr4. They provide the trailer nibblesT1-T4. The operation of each of the multiplexers 122b-122i isrespectively controlled by an individual one of control lines 122b-122i.The control lines 122b-122e are respectively designated asdataSelect(hdr1)-dataSelect(hdr4)). The control lines 122f-122i arerespectively designated as dataSelect(trlr1)-dataSelect(trlr4).

The operation of the multiplexer 106 in FIG. 12 may be seen from thefollowing examples. When the dataSelect(hdr1) signal on the line 122b isa binary 1, the hdr1 signal on the line 124b passes through themultiplexer 120b. The hdr1 signal actually constitutes the H1 nibble inthe header. Since the hdr1 signal is a nibble, a data multiplexercorresponding to the multiplexer 120b would be provided for each of thefour (4) binary bits in the header nibble H1. When the dataSelect(hdr1)signal is a binary 0, the output signal from the multiplexer 120a passesthrough the multiplexer 120b. Thus, if all of the data Select signals onthe lines 122b-122i constitute binary 0's, the received data (rxData)introduced to the multiplexer 120a passes through all of themultiplexers to a line 126 constituting the output of the multiplexer120i. The data on the line 126 is designated as xdata. In this way theoriginating device 30a either passes the received data (rxData) orsubstitutes header nibbles H1-H4 for the first four (4) nibbles of thepreamble and provides the four additional nibbles T1-T4 for the trailer.

The expansion controller and arbitration stage 104 in FIG. 11 is shownin additional detail in FIG. 13. It includes collision logic 130, anexpansion state machine 132, a collision timer 134 and interface logic136. The collision logic 130 receives the XCOLIN signal on the line 99a(see also FIGS. 9 and 11) and introduces a collision signal on a line138 to the expansion state machine 132. The expansion state machine 132also has an input from the received data valid (rxdv) line 112a (alsoshown in FIG. 11) and provides an output on the dataSelect lines122a-122i to the data multiplexers 120a-120i in FIG. 12.

The expansion state machine 132 also provides a count enable (counten)signal on a line 140 and a count down (countdn) signal on a line 142.The count enable signal on the line 140 initiates the CollisionResolution Time indicated at 95 in FIG. 20. The count down signal on theline 142 decrements the Collision Resolution Time on a periodic basis toindicate at each instant the period that remains in the CollisionResolution Time 95.

The signal on the received data valid (rxdv) line 112a is alsointroduced to the interface logic 136. The interface logic 136 alsoreceives a drv out signal on a line 144 from the expansion state machine132. The drv out signal indicates the end of the Collision ResolutionTime. The interface logic 136 provides a plurality of outputs: (1) thedata valid (xdv) signal 60 in FIGS. 4, 7 and 20, (2) the collision(xerr) indication 70 in FIG. 20, (3) the xclk signal 92 in FIGS. 7 and20, (4) the XCOLOUT indication on the line 96a (also shown in FIGS. 9and 11) and (5) the XCRSOUT indication 84a (also shown in FIGS. 9 and11).

The Expansion State Machine 132 in FIG. 13 is shown in additional detailin FIG. 14 in the form of a flow chart or diagram. The flow chartincludes an idle block 150 which activates a WAIT₋₋ BCMI stage 152 toobtain the production of the XCRSOUT signal 90 in FIG. 20 and initiatethe production of the Collision Resolution Time indicated at 95 in FIG.20. The stage 152 then initiates the downward counting on a periodicbasis of the Collision Resolution Time 95.

During the period of the countdown, the stage 152 sends a collisionsignal to a COL₋₋ BCM stage 154 if a collision is indicated. The stage154 then sets all of the dataSelect(all) signals in FIG. 12 to 0 toprovide for the operation of the multiplexers 120a-120i in FIG. 12 inthe idle state. The expansion state machine 132 then remains in the idlestate during all of the time that the packet involved in the collisionis providing nibbles and thereafter until a new packet is received.

At the end of the Collision Resolution Time (95 in FIG. 20), the WAIT₋₋BCMI stage provides a signal on a line 156 provided that no collisionhas occurred in the time period 95 in FIG. 20. This causes the XDIR₋₋ 0signal 94 in FIG. 20 to be turned on and the production of the XCLKsignals 92 in FIG. 20 to be initiated. In successive ones of the XCLKsignals 92, the header nibbles H1, H2, H3 and H4 are generated as aresult of the generation of the control signals dataSelect(hdr1),dataSelect(hdr2), dataSelect(hdr3) and dataSelect(hdr4) on the lines122b, 122c, 122d and 122e (also shown in FIG. 12). However, if the datavalid signal 60 (FIGS. 4, 7 and 20) is not produced in any of theseclock signals, a signal is generated on a line 158 in FIG. 14 and isintroduced to the idle stage 150 to provide for an idle operation duringthe remaining time of the packet.

An RXDV₋₋ ACTIVE state is entered in an RXDV₋₋ ACTIVE stage in FIG. 14as a result of the rxdv input control signal causing the transition fromHDR.3 to RXDV₋₋ ACTIVE. When no data valid signal (!rxdv) signal 60 isbeing received and the dataSelect(trler) signal on the control line 122f(also shown in FIG. 12) is a binary 1, a SEND₋₋ FOOT1 stage 162 in FIG.14 produces a T1 nibble. In like manner, a SEND₋₋ FOOT2 stage 164, aSEND₋₋ FOOT3 stage 166 and a SEND₋₋ FOOT4 stage 168 produce the trailernibbles T2, T3 and T4 in response to control signalsuct/dataSelect(trlr2), uct/dataSelect(trlr3), and uct/dataSelect(trlr4)control signals, (the dataSelect(trlr2), dataSelect(trlr3) anddataSelect(trlr4) control signals also being shown in FIG. 12. The "uct"in the control signals specified above indicates that the transfer isunconditional and is not dependent upon any condition. When the trailernibbles T1-T4 have been produced, the stage 150 is set to the idle stateto wait until a new packet is provided. This is provided by a uct signalon a line 169.

The data forwarding stage 108 shown in FIG. 11 as a single block isshown in additional detail in FIG. 15. The blocks shown in FIG. 15include a start-of-frame detector (SFD) 170, a first-in-first-out (FIFO)controller 172 and a FIFO 174. The start-of-frame detector 170 receivesthe data valid (xdv) signals 60 (see also FIGS. 4, 7 and 20), the xclock(xclk) signals 92 (also shown in FIG. 20) and the xdata signals 104(also shown in FIG. 20) and produces a GOT SFD signal on a line 176.This signal indicates that the start-of-frame 16 in the packet 40 hasbeen detected. This signal activates the FIFO controller 172 whichproduces a fifoLoadenable signal on a line 178. The signal on the line178 enables the data to be loaded into the FIFO 174. The data issubsequently transferred from the FIFO 174 for the originating device30a on the txdata line 118a also shown in FIG. 11.

FIG. 16 shows a start-of-frame detect machine generally indicated at180. The state machine 180 may be considered as a part of thestart-of-frame detect stage 170 in FIG. 15. The state machine 180 may beconsidered to include an idle state 182, a GOT5 state 184 and a GOTSFDstate 186. A line 188 extending from the idle state 182 to the GOT5state 184 activates the GOT5 state when the line provides the data validsignal 60 (FIGS. 4, 7 and 20) and the xdata provides a hexadecimal valueof five (5) represented by a binary pattern of 0101.

A line 190 extending from the GOT5 state 184 to the GOTSFD state 186activates the GOTSFD state 184 when the line provides the data validsignal 60 (FIGS. 4, 7 and 20) and the xdata provides a hexadecimal valueof D (represented by a binary pattern of 1101). When this occurs, theoriginating device 30a processes the remainder of the packet and sendsan !xdv signal on a line 192 at the end of the packet to return the SFDState Machine to the idle state 182. As previously described, the !xdvstate occurs when the data valid signal 60 (FIGS. 4, 7 and 20) is nolonger produced.

The data processor 110 in FIG. 11 is shown in additional detail in FIG.17. The data processor 110 includes a data processing state machine 194and the statistics block 52. It also includes a plurality of registers196a-196f. The data valid (xdv) signal 60 (FIGS. 4, 7 and 20) and thecollision (xerr) signal 70 (FIGS. 7 and 20) are introduced to the dataprocessing state machine 194. The registers 196a-196c are respectivelydesignated as PGI1-PGI3 and the registers 196d-196f are respectivelydesignated as TRLR2-TRLR4. LoadHDR1, loadHDR2 and loadHDR3 signals arerespectively introduced to the registers 196a-196c from the dataprocessing state machine 194 and loadTRLR2, loadTRLR3 and loadTRLR4signals are respectively applied to the registers 196d-196f. The signalsfrom the registers 196a-196f are introduced to the statics stage 52 forrecording in this stage.

Header signals for the H2 nibble are not introduced from the dataprocessing state machine 194 to a register corresponding to theregisters 196-196c because all of the binary bits for the header nibbleH2 are 0. (See FIG. 3.) Similarly, trailer signals for the T1 nibble arenot introduced from the data processing state machine 194 to a registercorresponding to the registers 196d-196f because all of the binary bitsfor the trailer nibble T1 are 0. (See FIG. 5.)

FIG. 18 is a flow chart or diagram showing the operation of the dataprocessing state machine 194 in FIG. 17. As a first operation, anunconditional (uct) transfer is provided from a Save state 210 to aStart state 212. When there is a data valid (xdv) signal 60 (FIGS. 4, 7and 20), the header nibble Hi is loaded into the packet 40 as shown at214. An advance is then made to header nibble 2, as indicated at 216,when there is a data valid (xdv) signal.

Nothing is loaded in header nibble 2 because there are all binary 0's inheader nibble H2 (see FIG. 3). When there is a data valid (xdv) signal60, an advance is then made to load header nibble H3 as indicated at 218in FIG. 18. Thereafter an advance is made, as indicated at 220, to loadheader nibble H4 when there is a data valid signal (xdv) 60. If there isno data valid signal to load any of the data nibbles H1, H2, H3 and H4,a return is made to the start state 212 as indicated at 222 in FIG. 18.A "no data" valid signal is indicated at !xdv in FIG. 18.

When there is no collision signal 70 (see FIG. 7), the trailer T1 isloaded as indicated at 224. A "no collision" signal is indicated at!xerr in FIG. 18. When there is no collision signal 70 (see FIG. 4), theTrailer T2 is loaded as indicated at 226. If there is a collisionsignal, a binary "1" is produced in the trailer T2 (see the XERR columnin FIG. 8), and a return is made to the start state 210 as indicated at228 in FIG. 18. If there is not a binary "1" in the XERR column for thetrailer T2 in FIG. 8 to indicate a collision, the trailer T3 isunconditionally loaded, as indicated at 230, in accordance with the loadTRLR3 signal. Similarly, the trailer T4 is unconditionally loaded, asindicated at 232, in accordance with the load TRLR signal. When thisloading has been completed, a return is made to the Save state 210 asindicated at 232 in FIG. 18.

Although this invention has been disclosed and illustrated withreference to particular embodiments, the principles involved aresusceptible for use in numerous other embodiments which will be apparentto persons of ordinary skill in the art. The invention is, therefore, tobe limited only as indicated by the scope of the appended claims.

What is claimed is:
 1. In combination for use with a plurality oforiginating devices and a plurality of ports on each of the originatingdevices in sending packets of binary coded signals, each packetincluding binary coded signals representing a preamble, a start-of-framedelimiter and data,means at an individual one of the originatingdevices, and at an individual one of the ports in such originatingdevice, for receiving such packets, and means at the individual one ofthe originating devices for modifying a first portion of the preamble toprovide a header indicating the individual one of the originatingdevices and the individual one of the ports in such individual one ofthe originating devices, means at the individual one of the originatingdevices for transmitting the header, the remaining portion of thepreamble, the start-of-frame delimiter and the data to other ones of theoriginating devices in the plurality, the packets being formed fromsuccessive nibbles each defined by a plurality of binary bits, themodifying means being operative to provide a last nibble in the headerand a first nibble in the second portion of the preamble in a patterndistinguishing the header and the second portion of the preamble fromthe start-of-frame delimiter, the packet including informationspecifying a particular one of the originating devices to receive thepacket, means at the particular one of the originating devices forsubstituting the modified portion of the preamble in place of theheader, means at the particular one of the originating devices fortransmitting the packet including the preamble, the start-of-framedelimiter and the data, an observing station for receiving the packetwith the header, the second portion of the preamble, the start-of-framedelimiter and the data, means at the observing station for processingthe header to determine the individual one of the originating devicesand the individual one of the ports in such individual one of theoriginating devices, and means at the observing station for making arecord of the individual one of the originating devices and theindividual one of the ports in the individual one of the originatingdevices.
 2. In combination at an individual one of a plurality oforiginating devices for receiving and processing packets of binary codedsignals, each packet including binary coded signals representing aheader, a first portion of a preamble having a particular format, astart-of-frame delimiter and data including the source of the packet andthe individual one of the originating devices as a recipient of thepacket,means for receiving the packet, means responsive to the dataindicating the individual one of the originating devices as a recipientof the packet for providing for a processing of the binary coded signalsin the packets, means responsive to the header in the packets forsubstituting the particular format of the first portion of the preamblefor the header in the packets, and means for transmitting the packetsincluding the first portion of the preamble in the particular format,the start-of-frame delimiter and the data.
 3. In a combination as setforth in claim 2 whereinthe particular format of the header constitutesa first particular format and wherein the start-of-frame delimiter has asecond format different from the first format and wherein the header isformed from a plurality of nibbles each defined by a plurality of binarybits and wherein a last nibble in the header and a first nibble in asecond portion of the preamble have a format different from the secondformat and wherein means are provided for distinguishing the last nibblein the header and the first nibble in the second portion of the preamblefrom the start-of-frame delimiter.
 4. In combination for use with anindividual one of originating devices in a plurality, and an individualone of a plurality of ports in the individual one of the originatingdevices, for receiving and processing packets of binary coded signals,each packet including, after such processing a header, for identifyingthe individual one of the originating devices and the individual one ofthe ports in the individual one of the originating devices, a portion ofa preamble having a particular format, a start-of-frame delimiter, anddata,an observing station displaced from the originating devices forreceiving the packets from the individual one of the ports in theindividual one of the originating devices, a processor responsive at theobserving station to the header for determining the individual one ofthe originating devices and the individual one of the ports in theindividual one of the originating devices, wherein the header is formedfrom a plurality of nibbles each defined by a plurality of binary bitsand the preamble portion is formed from a plurality of nibbles definedby a plurality of binary bits and wherein a last nibble in the header ischosen so that such last nibble and the preamble portion have a formatdifferent from any two (2) nibbles in the header and wherein means areprovided at the observing station for distinguishing the last nibble inthe header and a first nibble in the preamble portion from any two (2)nibbles in the header.
 5. A method of indicating an individual one of aplurality of originating devices, and an individual one of a pluralityof ports in such individual one of the originating devices, forreceiving packets of signals from an external source, each of thepackets being formed from a plurality of nibbles and including a header,a preamble portion, a start-of-frame delimiter and data, the headerindicating the individual one of the plurality of originating devicesand indicating the individual one of the ports in the individual one ofthe indicating devices, including the steps of:receiving the packet atan observing station, processing at the observing station the headers inthe packets to determine the individual one of the originating devicesand the individual one of the ports in the individual one of theoriginating devices, making a record of the individual one of theoriginating devices and the individual one of the ports in theindividual one of the originating devices, receiving the packets at theother ones of the originating devices in the plurality, converting theheaders in the packets at such other ones of the originating devices inthe plurality to the preamble, the preamble being formed from aplurality of nibbles each having a particular pattern, the header beingformed from a plurality of nibbles, and the conversion of the nibbles inthe header at such other ones of the originating devices to the preamblebeing in the particular pattern.
 6. A method of indicating an individualone of a plurality of originating devices, and an individual one of aplurality of ports in such individual one of the originating devices,for receiving packets of binary coded signals from an external source,each of the packets being formed from a plurality of nibbles andincluding a header, a preamble portion, a start-of-frame delimiter anddata, the header indicating the individual one of the plurality oforiginating devices and indicating the individual one of the ports inthe individual one of the indicating devices, including the stepsof:receiving the packets at other ones of the originating devices in theplurality, converting the headers in the packets at such other ones ofthe originating devices in the plurality to the preamble portion, thepreamble portion being formed from a plurality of nibbles each having aparticular pattern, the header being formed from a plurality of nibbles,and the conversion of the nibbles in the header at such other ones ofthe originating devices to the preamble portion being in the particularpattern.
 7. In combination for use with a plurality of originatingdevices and a plurality of ports on each of the originating devices insending packets of binary coded signals to other originating devices inthe plurality, each packet including binary coded signals representing apreamble, a start-of-frame delimiter and data,a sender in each of theoriginating devices for sending packets from such originating device toother originating devices in the plurality, means in each of theoriginating devices for providing a trailer at the end of each packet,and an encoder in each of the originating devices for indicating in thetrailer in each packet from such originating device whether or not suchoriginating device has experienced a collision in the sending of suchpacket from such originating device with the sending of a packet fromanother of the originating devices in the plurality.
 8. In a combinationas set forth in claim 7 whereinthe encoder in each of the originatingdevices is operative to indicate in the trailer from such originatingdevice whether or not each packet from such originating device is anormal packet.
 9. In a combination as set forth in claim 7 wherein theencoder in each of the originating devices is operative to indicate inthe trailer from such originating device whether or not such packet isfrom an acceptable source.
 10. In a combination as set forth in claim 7wherein the encoder in each of the originating devices is operative toindicate in each of the trailers from such originating device the spacebetween the end of such packet and the beginning of the next packet. 11.In a combination as set forth in claim 7,an observing station forreceiving the packets with the preamble, the start-of-frame limiter, thedata and the trailer, a processor in the observing station forprocessing the trailer in each packet from such originating device todetermine if a collision is indicated in such trailer between thesending of such packet from such originating device and a simultaneoussending of a packet from another one of the originating devices, and arecorder for recording an occurrence of collisions in the processedtrailers from such originating device.
 12. In a combination as set forthin claim 7,the encoder in each of the originating devices beingoperative to indicate in the trailer for each packet from suchoriginating device whether or not such packet from such originatingdevice is a normal packet, an observing station for receiving thepackets with the preamble, the start-of-frame limiter, the data and thetrailer, a processor in the observing station for processing the trailerin each packet from such originating device to determine if such packetis a normal packet, and a recorder for recording, in response toprocessing of the trailer in each packet from such originating device,whether or not such packet is normal.
 13. In a combination as set forthin claim 7,each packet being defined by a plurality of successivenibbles, the encoder in each of the originating devices being operativeto indicate in the trailer for each packet from such originating devicewhether or not such packet from such originating device is a runt packethaving a number of nibbles less than a particular number, an observingstation for receiving the packets with the preamble, the start-of-framelimiter, the data and the trailer, a processor in the observing stationfor processing the trailer in each packet to determine if such packet isa runt packet, and a recorder for recording, in response to processingof the trailer in each packet from such originating device, whether ornot such packet is a runt packet.
 14. In a combination as set forth inclaim 7,the encoder in each of the originating devices being operativeto indicate in the trailer for each packet from such originating devicewhether or not such packet is from an acceptable source, an observingstation for receiving the packet with the preamble, the start-of-framelimiter, the data and the trailer, a processor in the observing stationfor processing the trailer in each packet from such originating deviceto determine if the packet contains a start-of-frame delimiter, and arecorder for recording, in response to processing of the trailer in eachpacket from such originating device, whether or not the packet containsa start-of-frame delimiter.
 15. In a combination as set forth in claim7,the encoder in each of the originating devices being operative toindicate, in the trailer for each packet form such originating device, aspace between the end of each packet and the beginning of the nextpacket, an observing station for receiving the packet with the preamble,the start-of-frame limiter, the data and the trailer, a processor in theobserving station for processing the trailer in such packet from suchoriginating device to determine a space between the end of such packetand the beginning of the next packet, and a recorder for recording, inresponse to processing of the trailer in each packet from suchoriginating device, the space between the end of such packet and thebeginning of the next packet.
 16. In combination for use with aplurality of originating devices and a plurality of ports on each of theoriginating devices in sending packets of binary coded signals, eachpacket including binary coded signal representing a preamble, astart-of-frame delimiter and data,means at the individual one of theoriginating devices, and at an individual one of the ports in suchoriginating device, for receiving such packets, means at the individualone of the originating devices for modifying a first portion of thepreamble to provide a header indicating the individual one of theoriginating devices and the individual one of the ports in suchindividual one of the originating devices; each packet also including atrailer at the end of the packet, the trailer in each packet providingan indication of whether or not a collision has occurred between thesending of such packet by the individual one of the originating devicesand a simultaneous sending of another packet by one of the originatingdevices other than the individual one of the originating devices, andmeans for processing the trailer in each packet from such individual oneof the originating devices to determine whether or not a collision hasoccurred between the sending of such packet by the individual one of theoriginating devices and the simultaneous sending of another packet byone of the originating devices other than the individual one of theoriginating devices.
 17. In a combination as set forth in claim 7,eachpacket also including a trailer at the end of the packet, the trailer ineach packet providing an indication of whether or not a collision hasoccurred between the sending of such packet by the individual one of theoriginating devices a the simultaneous sending of another packet by oneof the originating devices other than the individual one of theoriginating devices, and means for processing the trailer to determinewhether or not a collision has occurred between the sending of suchpacket by the individual one of the originating devices and thesimultaneous sending of another packet by one of the originating devicesother than the individual one of the originating devices.
 18. In acombination as set forth in claim 16,the trailer in each packetproviding an indication of at least one of the following: (a) whether ornot such packet is a normal packet, (b) whether or not such packet is arunt packet, (c) whether or not such packet is from an acceptablesource, (d) whether or not such packet includes a start-of-framedelimiter and (e) a space between the end of such packet and thebeginning of the next packet from such individual one of the originatingdevices, and means for processing the trailer in each packet from theindividual one of the originating devices to determine at least one ofthe following: (a) whether or not such packet is a normal packet, (b)whether or not such packet is a runt packet, (c) whether or not suchpacket is from an acceptable source, (d) whether or not such packetincludes a start-of-frame delimiter and (e) the space between the end ofeach packet and the beginning of the next packet from such individualone of the originating devices.
 19. In a combination as set forth inclaim 17,the trailer in each packet providing an indication of at leastone of the following: (a) whether or not such packet is a normal packet,(b) whether or not such packet is a runt packet, (c) whether or not suchpacket is from an acceptable source, (d) whether or not such packetincludes a start-of-frame delimiter and (e) a space between the end ofeach packet and the beginning of the next packet from such individualone of the originating devices, means for processing the trailer todetermine at least one of the following: (a) whether or not such packetis a normal packet, (b) whether or not such packet is a runt packet, (c)whether or not such packet is from an acceptable source, (d) whether ornot such packet includes a start-of-frame delimiter and (e) the spacebetween the end of each packet and the beginning of the next packet fromsuch individual one of the originating devices.
 20. In combination foruse with a plurality of originating devices and a plurality of ports oneach of the originating devices in sending packets of binary codedsignals, each packet including binary coded signals representing apreamble, a starter frame delimiter and data,means at an individual oneof the originating devices, and at an individual one of the ports insuch originating device, for receiving such packets, means at theindividual one of the originating devices for modifying a first portionof the preamble to provide a header indicating the individual one of theoriginating devices and the individual one of the ports in suchindividual one of the originating devices, an observing stationdisplaced from the originating devices for receiving the packets fromthe individual one of the ports in the individual one of the originatingdevices, means at the observing station for processing the headers inthe packets to determine the individual one of the originating devicesand the individual one of-the ports in such individual one of theoriginating devices; each packet including a trailer at the end of thepacket, the trailer in each packet providing an indication of whether ornot a collision has occurred between the sending of such packet by theindividual one of the originating devices and a simultaneous sending ofanother packet by one of the originating devices other than theindividual one of the originating devices; means for processing thetrailer in each packet to determine whether or not a collision hasoccurred between the sending of such packet by the individual one of theoriginating devices and the simultaneous sending of another packet byone of the originating devices other than the individual one of theoriginating devices.
 21. In a combination as set forth in claim 20,meansat the observing station for providing a recording of the determinationprovided by the processing of the trailer in each packet.
 22. In acombination as recited in claim 4,each packet including a trailer at theend of the packet, the trailer in each packet providing an indication ofwhether or not a collision has occurred between the sending of suchpacket by the individual one of the originating devices and thesimultaneous sending of another packet by one of the originating devicesother than the individual one of the originating devices; means forprocessing the trailer in each packet to determine whether or not acollision has occurred between the sending of such packet by theindividual one of the originating devices and the simultaneous sendingof another packet by one of the originating devices other than theindividual one of the originating devices.
 23. In a combination as setforth in claim 22,means at the observing station for providing arecording of the determination provided by the processing of the trailerin each packet.
 24. In a combination as set forth in claim 22,thetrailer in each packet providing an indication of at least one of thefollowing: (a) whether or not such packet is a normal packet, (b)whether or not such packet is a runt packet, (c) whether or not suchpacket is from an acceptable source, (d) whether or not such packetincludes a start-of-frame delimiter and (e) a space between the end ofsuch packet and the beginning of the next packet from such individualone of the originating devices, and means for processing the trailer ineach packet from the individual one of the originating devices todetermine at least one of the following: (a) whether or not such packetis a normal packet, (b) whether or not such packet is a runt packet, (c)whether or not such packet is from an acceptable source, (d) whether ornot such packet includes a start-of-frame delimiter and (e) the spacebetween the end of each packet and the beginning of the next packet fromsuch individual one of the originating devices.
 25. In a combination asset forth in claim 23,the trailer in each packet providing an indicationof at least one of the following: (a) whether or not such packet is anormal packet, (b) whether or not such packet is a runt packet, (c)whether or not such packet is from an acceptable source, (d) whether ornot such packet includes a start-of-frame delimiter and (e) a spacebetween the end of each packet and the beginning of the next packet fromsuch individual one of the originating devices, and means for processingthe trailer to determine at least one of the following: (a) whether ornot such packet is a normal packet, (b) whether or not such packet is arunt packet, (c) whether or not such packet is from an acceptablesource, (d) whether or not such packet includes a start-of-framedelimiter and (e) the space between the end of each packet and thebeginning of the next packet from such individual one of the originatingdevices.
 26. A method as set forth in claim 5, including the stepsof:each packet also including a trailer at the end of the packet, thetrailer in each packet providing an indication of whether or not acollision has occurred between the sending of such packet by theindividual one of the originating devices and a simultaneous sending ofanother packet by one of the originating devices other than theindividual one of the originating devices, and processing the trailer ineach packet from such individual one of the originating devices todetermine whether or not a collision has occurred between the sending ofsuch packet by the individual one of the sending devices and thesimultaneous sending of another packet by one of the originating devicesother than the individual one of the originating devices.
 27. A methodas set forth in claim 26, including the step of:the trailer in eachpacket providing an indication of at least one of the following: (a)whether or not such packet is a normal packet, (b) whether or not suchpacket is a runt packet, (c) whether or not such packet is from anacceptable source, (d) whether or not such packet includes astart-of-frame delimiter and (e) a space between the end of each packetand the beginning of the next packet from such individual one of theoriginating devices, processing the trailer in each packet from theindividual one of the originating devices to determine at least one ofthe following: (a) whether or not such packet is a normal packet, (b)whether or not such packet is a runt packet, (c) whether or not suchpacket is from an acceptable source, (d) whether or not such packetincludes a start-of-frame delimiter and (e) the space between the end ofeach packet and the beginning of the next packet from such individualone of the originating devices.